1. Field of the Invention
This invention relates to a method for forming thin films which are used in semiconductor devices.
2. Description of the Prior Art
A titanium nitride (TiN) or titanium oxide nitride (TiON) film has been used as a layer, for example, for intimately contacting a substrate of a semiconductor device and an electrode therewith.
For contacting the substrate and the electrode, there are known techniques wherein a plug is formed in a contact hole. One such technique is a burying technique using so-called blanket tungsten (hereinafter abbreviated as BLK-W).
This burying technique is described with reference to the FIGS. 5(A) to 5(C) which illustrate the formation process.
As is particularly shown in FIG. 5(A), a diffusion layer 62 is formed in a semiconductor substrate 61 (made, for example, of monocrystal silicon). Thereafter, an insulating film 63 is formed on the semiconductor substrate 61. The insulating film 63 at its portion which has been formed on the diffusion layer 62 is provided with a contact hole 64 as shown.
As shown in FIG. 5(B), a contact layer 65 made, for example, of TiN is formed according to a chemical vapor deposition (CVD) process in such a way that inner walls of the contact hole 64 and the upper surface of the insulating film 63 are covered with the contact layer 65.
Finally, as shown in FIG. 5(C), a BLK-W film 66 is formed on the inside of the contact hole 64 and on the contact layer 65, for example, according to the CVD process.
If a tungsten (W) plug (not shown) is formed, the BLK-W film 66 is etched back, thereby leaving the BLK-W film 66 in the inside of the contact hole 64 to form a tungsten plug.
However, a disadvantage with the burying technique using the BLK-W is that if the contact hole 64 is not fully covered with the contact layer 65, there will be produced a void 67 (see FIG. 6) in the BLK-W film 66 which has been formed according to the CVD process.
Moreover, where titanium chloride (TiCl.sub.4) is employed as a source for the formation of a TiN film as the contact layer 65 according to the CVD process, chlorine (Cl) may be included in the thus formed contact layer 65. This will degrade the contact layer and lower its barrier property. In addition, the TiN film causes the contact resistance between the bottom of the contact hole 64 and the diffusion layer 62 to be undesirably increased.
Alternatively, if a titanium oxide nitride (TiON) film is formed as the contact layer 65 according to the CVD process, the problem of the chlorine inclusion in the contact layer 65 is solved but another problem of increasing the contact resistance is left unresolved. Thus, the contact resistance is undesirably increased in either case.
To avoid the above problem, it is usual to first form a titanium (Ti) film by sputtering and then a TiON film according to the CVD process. By this, the contact resistance is reduced with an improved barrier property. Since, however, the Ti film is formed by sputtering and the TiON film is formed by the CVD process, the throughput is considerably lowered.